Seriously, When Will the Heat End?

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After an unusually oven-like June, the beginning of July has been
sweltering, too. The heat didn't even take time off for
Independence Day, with 262 daily high records tied or broken
nationwide, mostly in the Midwest and the South, according
to government records. In comparison, only 60 records were set on
July 4, 2011, and a mere 15 were set on that date in 2010.

In addition to extreme heat during the day, it's not cooling off
very much at night; in the first four days of July, 432 daily
minimum high temperatures have been set (minimum high
temperatures generally reflect nighttime conditions).

But there's a small amount of good news for those who are cooking
in Chicago or withering in Washington, D.C. (both of which nearly
broke all-time highs yesterday): a "cold" front will be
sliding east across the country, said National Weather Service
meteorologist Greg Carbin. That should bring slightly cooler
weather and possibly precipitation to the Midwest and surrounding
areas by the beginning or middle of next week, Carbin told
OurAmazingPlanet.

In addition to the front, the
North American monsoon has arrived and is expected to lower
temperatures by about 20 degrees Fahrenheit (11 degrees Celsius)
in Colorado this weekend, and bring some much-needed
precipitation to the area that will hopefully help fight
Colorado's raging wildfires, said Jeff Weber, a scientist with
the University Corporation for Atmospheric Research in Boulder,
Colo. This same system should bring lower temperatures and
rain to North and South Dakota, Iowa and northern Illinois next
week, he said.

Still, most areas east of the Rockies should expect average
summertime temperatures at best next week; and then it will
probably get worse in a few days. Weber said he expects a
basic pattern to repeat itself throughout the summer: rising heat
will generate in the Southwest and slowly roll across the
country, causing uncomfortably high temperatures in any given
area for about 10 days. Then a lower pressure system will move
through, providing some mild relief for about three to four
days. Then, another heat wave will come again, he said. And so
on. [ Harshest
Environments on Earth ]

The heat
burning up the country right now is due in part to a
persistent high-pressure system, also called a heat ridge or
dome, which parked itself over the mountain West, and has now
shifted east into the Midwest and Southeast. The system is stuck
in place, Weber said, because of a slowdown of the North Atlantic
Oscillation, a climate pattern that pulls weather patterns
eastward across the country.

This "blocking" of the Atlantic has caused the jet stream, which
normally ferries air from west to east across the United States,
to buckle and trap heat in the Midwest and Southeast, Weber said.

It looks like the epicenter for heat this year will be the state
of Missouri and its surroundings, he said. And the heat dome
doesn't look likely to completely dislodge itself for the
remainder of the summer. Above-average temperatures are expected
throughout the central and eastern parts of the country
(excluding the northeastern states of Vermont, New Hampshire and
Maine), Carbin said.

The high nighttime temperatures that this system has brought are
dangerous for those sensitive to extreme heat. They are made
worse by the
urban heat island effect, wherein buildings and man-made
materials absorb more heat during the day and emit it at night,
Carbin said. It's also exacerbated by air pollution, which
prevents heat from dissipating into the upper atmosphere.

High and dry

The warm summer follows
an unusually warm winter, which was the hottest and driest
that the western United States has ever recorded.

The first five months of 2012 have also been the hottest on
record in the contiguous United States. And that's not including
June, when 164 all-time high temperature records were tied or
broken around the country, according to government records.

The early heat records are unusual, since July and August tend to
be the hottest summer months in most areas of the country, said
Jake Crouch, a climate scientist with the National Climatic Data
Center.

Dry soils, in part a product of the dry winter, exacerbate the
heat. "If the soils were wetter, more energy would be absorbed by
the water and the daily high temperatures wouldn't be as warm,"
Crouch told OurAmazingPlanet. For example, southern Georgia and
Florida, drenched by Tropical Storm Debby, haven't been as hot as
areas to the north in the last week or so.

Carbin went further, saying that this persistent high heat —
stretching back through the winter —and extended drought
nationwide are the exact features predicted to occur in a warming
world. "An increasing frequency of heat waves, that's one aspect
of climate change you can point to," Carbin said.